Razor blades and other thin cutting edge tools and method of manufacture of such tools

ABSTRACT

A HOT ROLLED STEEL STRIP CONTAINING 14% CHROMIUM IS ANNEALED AT 825*C. FOR AT LEAST TWO HOURS AND THEN COOLED. THE ANNEALED STRIP IS THEN COLD ROLLED IN SEVERAL STEPS WITH INTERMEDIATE RECRYSTALLIZATION ANNEALINGS TO A THICKNESS OF ABOUT 0.2 MM. THEN THE STRIP IS AUSTENITIZED AT A TEMPERATURE OF 1140*C. FOR ABOUT 5 SECONDS AND THEN QUENCHED TO PRODUCE A MARTENSITE AND AUSTENITE MIXTURE WITH AN AUSTENITE CONTENT OF ABOUT 60%. THE STRIP IS THEN HEATED AT 710*C. FOR TWO HOURS PRODUCING A PRECIPITATION OF FINE CARBIDE GRAINS IN A MATRIX OF FERRITE. AFTER FURTHER COLD ROLLING WITH INTERMEDIATE RECRYSTALLIZATION ANNEALINGS TO THE FINAL THICKNESS OF 0.1 MM., THE STRIP IS HEATED TO A TEMPERATURE OF ABOUT 1100*C., QUENCHED TO -80*C., AND ANNEALED AT ABOUT 200*C.; AN EDGE OF THE STRIP IS GROUND TO PROVIDE A SHARPENED RAZOR EDGE; AND A LAYER TO IMPROVE THE SHAVING PROPERTIES IS APPLIED TO THE SHARPENED EDGE IN A PROCESS INVOLVING HEATING THE STEEL TO A TEMPERATURE BETWEEN 200 AND 400*C.

April 29, 1971 JAN'CHRISTER- 1-1.0. CARLEN ETAL 3,575,737

HV 0.5 v

RAZOR BLADES AND OTHER THIN CUTTING EDGE TOOLS AND METHOD OF MANUFACTUREOF SUCH TOOLS Filed June 25, 1968 United States Patent 3,575,737 RAZORBLADES AND OTHER THIN CUTTING EDGE TOOLS AND METHOD OF MANUFAC- TURE OFSUCH TOOLS Jan-Christel Heuric Ovesson Carlen, Sandviken, Sweden, andFrancis Edward Flaherty, Canton, Mass., assignors to Sandvikens.Iernverks Aktiebolag, Sandviken, Sweden Filed June 25, 1968, Ser. No.739,831 Int. Cl. (121d 9/18 U.S. Cl. 14812.4 16 Claims ABSTRACT OF THEDISCLOSURE A hot rolled steel strip containing 14% chromium is annealedat 825 C. for at least two hours and then cooled. The annealed strip isthen cold rolled in several steps with intermediate recrystallizationannealings to a thickness of about 0.2 mm. Then the strip isaustenitized at a temperature of 1140 C. for about 5 seconds and thenquenched to produce a martensite and austenite mixture with an austenitecontent of about 60%. The strip is then heated at 710 C. for two hoursproducing a precipitation of fine carbide grains in a matrix of ferrite.After further cold rolling with intermediate recrystallizationannealings to the final thickness of 0.1 mm., the strip is heated to atemperature of about 1100 C., quenched to 80 C., and annealed at about200 C.; an edge of the strip is ground to provide a sharpened razoredge; and a layer to improve the shaving properties is applied to thesharpened edge in a process involving heating the steel to a temperaturebetween 200 and 400 C.

The present invention relates to a method for the manufacture of razorblades and similar thin cutting edge tools with high wear resistance andhigh hardness from hardenable chromium steels containing at least 8%chromium and which are cold worked to thin dimensions, preferably bycold rolling. The invention also comprises razor blades and othercutting edge tools made according to the method of manufacture.

In conventional manufacture of razor blades from hardenable steels, thesteel is subjected to a succession of annealing and cold workingoperations. Thus, the hotworked raw material is annealed so that thehotworked structure is transformed into a structure more suitable forcoldworking consisting of ferrite and carbides whereby the material atthe same time becomes soft enough to be coldworked. In coldworking thehardness increases, but by annealing the material after coldworking to acertain degree a recrystallization is achieved by which the materialagain becomes soft enough for continued coldworking. By alternatingcoldworking and recrystallization annealing the material is given adesired thin dimension. The structure achieved after the finalcoldworking will be dependent on how the annealing of the hotworkedmaterial was done as well as the annealing operations between thediiferent steps of coldworking. Longer time of annealing and/or higherannealing temperature gives a coarse grained carbide structure whileshort time and/ or low temperature gives a finegrained carbidestructure. As to the properties of the materials after the finalhardening, a finegrained carbide structure in many cases would bepreferred. However, materials with a finegrained carbide structure areexpensive and difiicult to coldwork as they are harder and brittler thanmaterials with coarse carbides and have considerably worsenedcoldworking properties.

The purpose of the present invention is to produce razor blades andother thin cutting edge tools with high wear resistance and highhardness from hardenable chromium steels containing at least 8% chromiumby giving the steel such a finegrained carbide structure that thehardening properties are greatly improved without in any appreciabledegree worsening the coldworking properties.

The steels for use in making the razor blades or cutting edge toolsaccording to the invention are of the type that contains at least 20%and preferably at least 40% residual austenite after complete orpractically complete carbide dissolution of austenitizing and asubsequent cooling to room temperature or less. The residual austeniteis usually also so stable that it will not disintegrate to any greatextent in conventional tempering operations (max. 450 C.).

The method according to the invention is substantially characterized inthat the steel after coldworking, i.e., coldrolling, is austenitized atsuch a high temperature that practically all of the carbide grains in itare completely dissolved, the steel thereafter being so rapidly cooledthat a mixture of austenite and martensite is obtained, then the steelis heat treated at a temperaure under the temperature for austenitizingbut above 600 C. and thereafter is hardened preferably after additionalcoldworking such as cold-rolling.

The coldworking before the austenitizing is usually done in severalsteps between which the steel is recrystallization annealed. Also, thecoldworking between the previously mentioned heat treatment and thehardening is usually carried out in two or more steps withrecrystallization annealings in between. The hardening temperature isdependent on the composition of the steel. It is usually chosen between8501l50 C. and often within the narrower interval l000ll50 C. Inhardening, the steel is cooled from hardening temperature to roomtemperature or less, i.e., within the range between -20 C. and C.Normally, the hardening is followed by a tempering between l00275 C. Thecutting edge is preferably formed after this tempering by grinding orsimilar methods. Then another tempering can be made, i.e., in connectionwith application of a coating to the cutting edges to improve theshaving properties. The last-mentioned tempering occurs usually in alimited time period at a temperature exceeding C., i.e., between 150-250 C., and in certain cases up to 400 C. Immediately before thehardening the strip steel is often shaped, i.e., by stamping.

In manufacturing the razor blades and the cutting edge tools accordingto the invention, a hardenable chromium (steel is used which, asmentioned earlier, contains at least 8% chromium and which preferablyhas been formed into a strip by hot-rolling. The hot-rolled strip isannealed, depending on the composition of the steel, at such atemperature, i.e., between 775875 C., that it obtains a coarse grainedstructure which is especially suitable for the subsequent coldworking.The coldworking which is usually done by cold-rolling is carried out inseveral steps with recrystallization annealings in between. When thesteel strip is coldworked to a dimension at or near the desired thinfinal dimension, i.e., a thickness between 0.1- 0.4 mm. preferably0.15-0.33 mm., a heat treatment is made characterized in that the steelstrip is austenitized at such a high temperature, i.e., more than 1000C. and preferably above 1100 C., that practically all occuring carbidegrains are totally dissolved and thereafter the steel strip is cooledpreferably to room temperature of eventually to lower temperatures. As aresult, the steel strip has a structure consisting of matensite andaustenite in which the austenite content usually lies between 20-l00%and in most cases between 4080%. By heat treating the steel strip afterthis at a compaartively low temperature, that is a temperature below thetemperature for austenitizing but above 600 C., a finely dispersedprecipitation of carbides in a matrix of ferrite is obtained.Thereafter, the strip can be finished in cold condition preferably bycold-rolling in one or more steps to the intended final dimension, i.e.,a thickness about 0.1 mm. One or more recrystallization annealings canalso be made during this coldworking. By the above-mentioned heattreatment, the material obtains a structure which is especially suitablefor the following hardening whereby a considerably higher hardness canbe achieved at the hardening than has earlier been possible inconventionally produced steels of the corresponding composition. Toachieve maximum hardness after the hardening, the material, according tothe invention, should normally be deep cooled to a temperature betweenand 120 C. and tempered to a temperature between 100-275 C. in which thehigher tempering temperature is used at short tempering times and thelower at long times, i.e., at least 15 minutes. As a result of thestructure and high hardness obtained through the invention, the shapingof the cutting edge by grinding or similar methods is facilitated. Whenthe cutting edge is shaped it is often coated with a layer whichimproves the shaving properties and this requires heating to atemperature above 150 C. Even if the hardness is somewhat decreased atsuch a heating, the razor blades and cutting edge tools according to theinvention will have a higher final hardness than conventionallymanufactured razor blades and cutting edge tools of the same chemicalcomposition.

The reason for the favorable results with the method according to theinvention will probably be explained by the following.

In hardening a high alloyed chromium steel, the structure is transformedfrom ferrite with carbides to martensite and depneding on the basicstructure and the hardening conditions to a certain amount of residualaustenite. Often the carbides are incompletely dissolved in thehardening heating so a certain amount of residual carbides are to befound in the hardened material. In austenitizing, whereby the carbidesare dissolved, the degree of carbide dissolution is determined partly bythe temperature and time and partly by the carbide structure of thebasic material. The carbides are rich in carbide forming elements suchas chromium, tungsten and vanadium and this causes that the matrix closeto the carbides to become rich in these elements upon carbidedissolution in austenitizing. In austenitizing, a certain equalizationof the percentages of the carbide forming elements between the areawhich surrounds the carbides and the rest of the matrix is obtained bydiffusion. However, this equalization advances at normal austenitizingtimes only to a limited extent thus causing the composition of thematrix to vary. As almost all alloying elements decrease the temperatureat which martensite begins to form, the areas rich in alloying elementsform martensite at a lower temperature and thus after hardening containa higher percentage of residual austenite than the remaining steel. Thisphenomenon is accentuated by the fact that the carbide forming alloyingelements also decrease the carbon activity causing the carbon in saidareas to be also enriched and to strongly contribute to increasing thepercentage of residual austenite in these areas.

In steels with finely dispersed precipitated carbides, the carbidedissolution in austenitizing occurs rapidly compared to a material withcoarse grained carbides. Moreover, the diffusion distances are reducedin steels with many and small carbides as compared to a steel with fewand big carbides and, as a result, the variations in composition in thesteel are reduced. A steel with finely dispersed precipitated carbidesthus can be hardened more rapidly to a high hardness and the necessaryhardening time is shorted. Also, by having better homogenity in thecomposition, a final product with considerably higher hardness isobtained after hardening than if a conventionally manufactured materialwith a coarse carbide structure has been used.

The method according to the invention can be applied to a plurality ofsuitable hardenable chromium steels with at least 8% chromium. It ischaracteristic of the steels that when austenitized at such hightemperatures that practically all occurring carbides are dissolved andthat the steel in the subsequent cooling to room temperature or lowerhas a structure of at least 20% and preferably at least 40% or moreresidual austenite and that this residual austenite is so stable that itwill not disintegrate to any considerable exent in conventionaltempering at temperatures up to 450 C.

In the heat treatment following the austenitizing, the steel shall beheated to a temperature below the temperature for austenitizing, i.e.,below 850 C. but above 600 C., and often above 700 C., and thereafterpreferably be cold-rolled to final thickness. However, normally thetemperature range for said heat treatment is chosen between 650 to 735C.

As examples of steel analyses suitable for the invention, the followingmay be given.

Percent C 0.3-1.0 Si 0-2 Mn 0-2 Cr 8-17 Mo 0-2 W 0-4 Additionally, V,Ti, Ta, Nb and Zr in sum totals altogether of 02% and Co, Cu, Ni, Be, Aland B in sum totals altogether of 0-3% and preferably 02% can beincluded.

The remainder is substantially all iron and the normally occurringimpurities in iron.

Percent Si -a 0.1-0.7

The remainder is substantially all iron and the normally occurringimpurities in iron.

Percent Additionally, Mo and/or W is included; the sum of the percentageof M0 and half of the percentage of W being 0.5-1.5%. The percentage Mowill amount to at most 1.5% and the percentage W to at most 3%. Theremainder is substantially all iron and the impuritiees normallyoccuring in iron.

The curves in FIGS. 1-4 show the hardness in Vickers (load 0.5 kg.) asfunction of the hardening temperature for steels treated conventionally(full lined/curves) and according to the invention (dash and dot linercurves) respectively.

The curves shown in FIGS. 1 and 2 refer to a stainless martensitic steelwith the composition 0.57% C., 0.38% Si, 0.39% Mn, 14.1% Cr and theremainder Fe. The steel having been hardened as strip with a thicknessof about 0.10 mm. from temperatures within the interval 100 C.- 1150 C.with a heating time of one minute and cooling to room temperature(curves 1 and 3) resp. to C. (curves 2 and 4).

The curves 1 and 2 show the hardnesses which are obtained in the earliernormal method of manufacture when a hot-rolled strip with a thickness ofabout 3 mm. after annealing was cold-rolled in several steps withintermediate recrystallization annealings to a final thickness of about0.1 mm. and thereafter was hardened. All annealings were made within theinterval 700-840 C.

Curves 3 and 4 show how a considerably higher hardness was achieved whena hot-rolled 3 mm. thick strip was treated according to the inventionand then hardened.

The treatment characteristic of the invention, i.e., austenitizing athigh temperature and a subsequent heat treatment at a lower temperature(about 710 C.) than the temperature for austenitizing was made when thethickness of the strip was about 0.2 mm.

When the steel strip was finished by rolling to a thickness of about 0.1mm., the hardening was made. The profit in hardness in this case wasmore than 100 Vickers (load 0.5 kg).

The FIGS. 3 and 4 show curves from a corresponding trial with a steelhaving the composition C= .63%, Si=1.12%, Mn=0.36%, Cr=10.5%, Mo=1.04%and the remainder iron.

Curves 5 and 6 show the hardnesses according to the conventional way ofmanufacture and curves 7 and 8 according to the method of the invention.Further, curves 5 and 7 represent the hardness after cooling to roomtemperature and curves 6 and 8 after cooling to -70 C. Also, for thissteel considerable improvement was achieved by applying the special heattreatment according to the invention. The profit in hardness was about95 Vickers (HV 0.5 kg.).

As an example of the method according to the invention the following maybe mentioned:

A hot rolled strip of a steel alloy containing in percent of weight0.60% C; 0.35% Si; 0.35% Mn; 14.0% Cr; balance Fe, was annealed at 825C. for at least two hours followed by a slow cooling, whereby astructure was obtained having coarse carbide grains. The annealed stripwas cold-rolled in several steps with intermediate recrystallizationannealings to a thickness of near the final thickness e.g. 0.2 mm. oralternatively to the final thickness of e.g. 0.1 mm. The strip wasthereafter austenitized at 1140 C. for about 5 seconds and then quenchedbetween blocks. Hereby the carbide grains were practically completelydissolved and a structure comprising a mixture of martensite andaustenite obtained, e.g. with an austenite content of about 60%. By aheat treatment for about 2 hours at 710 C. a precipitation of finecarbide grains in a matrix of ferrite was obtained. When the strip wascold-rolled to a thickness near the final thickness the strip wasfinished after said heat treatment by cold-rolling in one or more steps,possibly with intermediate recrystallization annealings to the intendedfinal thickness, e.g. 0.1 mm. By heating to a temperature of about -1l00C. followed by quenching to e.g. 80 C. and a possible subsequentannealing to about 200 C., a maximal hardness of about Vickers 800 (load0.5 kg.) is obtained, whereafter the edge or the edges are shaped bygrinding or similar methods. Finally the edge or the edges may be coatedwith a layer improving the shaving properties, which requires a furtherheating to a temperature, e.g. between ZOO-400 C.

While a particular embodiment of the invention has been shown anddescribed, various modifications thereof will be apparent to thoseskilled in the art and therefore it is not intended that the inventionbe limited to the disclosed embodiment or to details thereof anddepartures may be made therefrom within the spirit and scope of theinvention as defined in the claims.

What is claimed is:

1. Method for the manufacture of razor blades and similar thin cuttingedge tools with high wear resistance and high hardness from a hardenablechromium steel having a chromium content of at least 8%, Comprising thesteps of austenitizing the steel after cold working at such a hightemperature that practically all carbide grains occurring therein aredissolved, rapidly cooling the steel to obtain a mixed structure ofaustenite and martensite and then heat treating the steel at atemperature below the temperature for austenitizing, but above 600 C.

2. Method as claimed in claim 1 wherein said cold working before theaustenitizing is done in several steps, said steel being subjected torecrystallization annealing between said cold working steps.

3. Method as claimed in claim 1 further including the step subsequent tosaid heat treating step of hardening the steel by heating to atemperature within the range of 850-1150 C. followed by a quenchingstep.

4. Method as claimed in claim 3 wherein said steel is quenched to atemperature between 20 and C.

5. Method as claimed in claim 3 wherein said hardening step is followedby a tempering step at 100-275 C. whereafter a cutting edge is formed.

6. Method as claimed in claim 5 and further including the step oftempering the steel after forming of the cutting edge at a temperatureof more than C.

7. Method as claimed in claim 1, characterized in that said steel hasthe following composition: 0.3-1.0% carbon, 0-2% silicon, 02% manganese,817% chromium, 02% molybdenum, 0 4% tungsten, 02% altogether ofvanadium, titanium, tantalum, niobium and zirconium, 0-2% altogether ofcobalt, copper, nickel, beryllium, aluminum, and boron and the remainderconsisting substantially of iron.

8. Razor blades and other cutting edge tools, manufactured as claimed inclaim 1.

9. Method for the manufacture of razor blades and similar thin cuttingedge tools with high resistance and high hardness from a hardenablechromium steel having a chromium content of at least 8% comprising thesteps of austenitizing the steel to dissolve practically all the carbidegrains, rapidly quenching the steel strip to obtain a mixed structure ofaustenite and martensite, the austenite content being at least 20%,

and heat treating the steel strip of temperature above 600 C. but belowthe austenitizing temperature to obtain a precipitation of fine carbidegrains in a matrix of ferrite.

10. Method as claimed in claim 9 wherein said austenitizing temperatureis at least 1000 C.

11. Method as claimed in claim 9 and further including the steps ofsubjecting said steel strip to a first cold working operation beforeaustenitizing and a second cold working operation after heat treating,then hardening said steel strip by heating said strip to a temperaturewithin the range of 850-1150 C.; and forming a cutting edge on saidsteel strip.

12. Method as claimed in claim 11 and further including the step ofsubjecting said steel strip to a mechanical shaping operation betweenthe second cold working step and the hardening step.

13. Method as claimed in claim 11 further including a first temperingstep of heating said strip to a temperature of 100275 C. before formingsaid cutting edge and a second tempering step of heating said steelstrip to a temperature in excess of 150 C. after forming said cuttingedge.

14. Method as claimed in claim 11 wherein at least one of said coldworking operations is done in a series of steps, said steel strip beingsubjected to recrystallization annealing between said cold workingsteps.

15. Method as claimed in claim 14, characterized in that said steel iswithin the following range of compositions: OJ-1.0% carbon; 02% silicon;02% manganese; 817% chromium; 0-2% molybdenum; 0-4% tungsten; 02%altogether of vanadium, titanium, tantalum, niobium and zirconium; 0-2%altogether of cobalt, copper, nickel, beryllium, aluminum and boron; andthe remainder consisting substantially of iron.

8 16. Method as claimed in claim 15 wherein said 3,340,048 9/1967Floreen 148-12.3 austenitizing temperature is at least 1100 C. and saidheat 3,437,477 4/ 1969 McCune III 148-12.3 treating temperature is inthe range of 650-735 C. 3,469,972 9/1969 Carlen et a1. 75-126 3,473,97310/1969 Maekawa et a1 148-123 References 22 s 5 L. DEWAYNE RUTLEDGE,Primary Examiner UNITED STATES ENT W. W. STALLARD, Assistant Examiner2,999,039 9/1961 Lula et a1. 148-123 3,152,934 10/1964 Lula et a1148-12.4 US. Cl. X.R.

3,336,168 8/1967 Morita ct a1. 148-12.3 10 148143

